The present invention relates in general to phase shifters or phase modulators, particularly of the type used in radios. More specifically, the present invention provides a phase shifter/modulator utilizing a hybrid splitter terminated at both of its normal output ports with a reactive circuit; or a circulator terminated at its normal output port with a reactive circuit.
Mobile radio telephony frequently requires a phase modulator capable of modulating the phase of a carrier by large amounts. As an example of such a requirement, cellular mobile radio-telephone systems require a deviation of .+-.12 radians peak for a 1 kHz tone. This corresponds to a phase deviation of .+-.687.5 degrees peak modulation. Normally transmitters employ varicap (variable capacitance) modulators. This type of modulator uses the variation of phase shift of a detuned resonant circuit. Relative to the phase of the current at resonance, the current in a tuned circuit will vary from nearly +90 degrees to nearly -90 degrees. This theoretical maximum phase deviation of .+-.90 degrees (about 11/2 radians) is typically limited to .+-.1 radian where the phase variation with modulation voltage is nearly linear. In order to achieve a higher value of phase deviation, a low frequency carrier is phase modulated and then multiplied to achieve the correct operating frequency. One could also simply connect two phase modulators in tandem (series) to achieve the sum phase deviation.
The U.S. patent literature includes the following patents showing various circuits utilizing hybrid splitters and other such devices terminated by a reactive device or circuit. It is not intended to be an exhaustive list, but only a representative sample of patents.
U.S. Pat. No. 4,216,542--Hermesmeyer (Aug. 5, 1980)
U.S. Pat. No. 4,021,758--Standing (May 3, 1977)
U.S. Pat. No. 3,961,286--Kim (June 1, 1976)
U.S. Pat. No. 3,946,337--Philips et al (Mar. 23, 1976)
U.S. Pat. No. 3,798,573--Seidel (Mar. 19, 1974)
U.S. Pat. No. 3,745,250--Gerst (July 10, 1973)
U.S. Pat. No. 3,579,147--Brown (May 18, 1971)
U.S. Pat. No. 3,479,615--Garver (Nov. 18, 1969)
U.S. Pat. No. 3,440,570--Kasper (Apr. 22, 1969)
U.S. Pat. No. 3,440,342--Putnam (Sept. 3, 1968)
In addition, the patent literature includes the following U.S. patents relating to phase shift circuits. Again, this is not intended to be an exhaustive list, but merely a representative sample of patents.
U.S. Pat. No. 3,938,042--Gliever et al (Feb. 10, 1976)
U.S. Pat. No. 3,916,344--Enderby (Oct. 28, 1975)
U.S. Pat. No. 3,328,727--Lynk, Jr. (June 27, 1975)
U.S. Pat. No. 3,275,951--Maass (Sept. 27, 1966)
U.S. Pat. No. 3,267,393--Brossard et al (Aug. 16, 1966)
U.S. Pat. No. 3,196,368--Potter (July 20, 1965)
U.S. Pat. No. 3,101,452--Holcomb et al (Aug. 20, 1963)
None of the above-listed documents show a reflective-type phase shifter/modulator as set forth herein for achieving wide range phase shift.